ImageUtilities: use the new file writing methods.
ImageUtilities: use the new file writing methods.

We now ask stb_image_write and tinyexr to write to memory instead of the disk. Then we save their output to disk using our wrappers.


Former-commit-id: 8d2be9cea89cbdbe3765446cf7c1ad53bd93edb8
kosua20/GL_Template,kosua20/GL_Template